The production of algal biomass has increasingly been of interest. The potential usage of such material is found across a wide range of applications, including biofuel feedstock production, fertilizer, nutritional supplements, pollution control, and other uses.
For example, various approaches such as “open-air” and “closed-air,” have been considered for mass production of algal biomass. The United States Department of Energy conducted a program called the Aquatic Species Program from 1978 to 1996. The engineering efforts of the program were largely focused on large “open-air” racetrack pond designs. The ponds are so-named based on the fact that the culture medium is conveyed in a complete circuit in a continuous fashion. This flow of culture medium is achieved with large continuously turning paddle wheels, which induce a turbulent flow in the medium. The turbulent flow is necessary to mix the culture so that all algae cells receive sunlight. The ponds are similar in appearance to extremely elongated ovals.
“Closed-air” systems generally refer to systems that contain algal biomass production within a controlled environment, limiting exposure to outside air. Examples of such systems include closed photo-bioreactor structures forming a closed container for housing a culture medium for generating algal biomass. Having a controlled environment helps maximize the generation of algal material by limiting exposure to invasive species as well as controlling other environmental factors that promote algal growth. Similar to open-air systems, closed-air systems require the mixing of algal culture to maximize growth. It should be appreciated that industry standard practice for algal culture is to actively mix the culture.
Additionally, large algal culturing operations require large amounts of water to be transferred between culturing areas and processing areas. This incurs expense in terms of both pumping energy costs and pumping infrastructure capital cost.
Another area of similarity with both closed-air and open-air systems is that algal culture is typically dilute and must be extensively processed to extract the economically beneficial components of the algal cells. Because of this dilute nature of algal culture, often times 1 part in 1000 or less, the processing can be can be very expensive in terms of both capital cost and energy usage. In many cases, conventional processing equipment such as centrifuges and flocculation devices can cost more than the value of the algae that can be harvested over the lifetime of the equipment, and further, the energy required to operate the equipment can be greater than the energy embodied in the algae itself. In both of these two cases, the potential benefits of algal culture for biofuels cannot be realized because the energy and economic costs are too great.
It should be appreciated that a need exists to concentrate the algae culture in a cost effective and energy efficient manner prior to processing in order to maximize the potential benefits of algal culture. The present invention fulfills this need and others.